Describe poker chipping, and explain how it can be prevented. ...

[renzo156]

Describe poker chipping, and explain how it can be prevented.
 
  What will be an ideal response?

Question 2

Explain why coining can be used to make more complicated shapes than can conventional sintering.
 
  What will be an ideal response?

Question 3

A thermoformed part has a total surface area of 1000 cm2 and a required thickness of 1mm. It is formed from a blank sheet with a total usable surface area of 500 cm2 (not counting the part of the sheet used for clamping) and a thickness of 2 mm. When forming the part, the walls often tear. Indicate what might be the problem.
 
  What will be an ideal response?

[elizabethrperez]

Answer to Question 1

Poker chipping occurs in the ram extrusion process when the charges of compacted resin are not well bonded together. The billet made by the ram extrusion process can therefore be in separate charge portions. These are compacted together like discs or poker chips. This problem can be prevented by improving the consolidation between charges, usually done most easily by increasing the fusion temperature.

Answer to Question 2

In conventional sintering the shape of the part is determined by the preforming mold. Since the main purpose of preforming is to eliminate voids and compact the material, high pressures are required and the ability to press the powdered material into complicated shapes is compromised. In coining, the part is placed

into a mold when the part is in a softened state. Therefore, pressing into a detailed shape is much easier.

Answer to Question 3

The area ratio of 1:2 indicates that the thickness will be reduced from 2 mm to 1 mm in the final part, assuming that the wall thicknesses are uniform. Uniform wall thicknesses are not likely with thermoforming and so some portions of the walls will be much thinner than the required 1 mm and will be likely to rupture when drawn.